get_user_page, get_user_pages_fast
get_user_page, get_user_pages_fast用于获取用户buffer所mapped的页。
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @write: whether pages will be written to
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
*
* Attempt to pin user pages in memory without taking mm->mmap_sem. <==不需要获取锁， get_user_pages_fast调用这个函数进行获取当前进程的页，这个函数不锁mm的
* If not successful, it will fall back to taking the lock and
* calling get_user_pages().
*
* Returns number of pages pinned. This may be fewer than the number
* requested. If nr_pages is 0 or negative, returns 0. If no pages
* were pinned, returns -errno.
*/
int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages)
Example：
1，get_user_pages_fast
/* TODO: This is really inefficient. We need something like get_user()
* (instruction directly accesses the data, with an exception table entry
* returning -EFAULT). See Documentation/x86/exception-tables.txt.
*/
static int set_bit_to_user(int nr, void __user *addr)
{
unsigned long log = (unsigned long)addr;
struct page *page;
void *base;
int bit = nr + (log % PAGE_SIZE) * 8;
int r;
r = get_user_pages_fast(log, 1, 1, &page);
if (r < 0)
return r;
BUG_ON(r != 1);
base = kmap_atomic(page);
set_bit(bit, base);
kunmap_atomic(base);
set_page_dirty_lock(page);
put_page(page);
return 0;
}
2，get_user_pages
down_read(¤t->mm->mmap_sem); <==需要获取锁
res = get_user_pages(current, current->mm,
(unsigned long)buf,
1,
1,
0,
&page,
NULL);
if (res) {
printk(KERN_INFO "Got mmaped.\n");
myaddr = kmap(page);
printk(KERN_INFO "%s\n", myaddr);
strcpy(myaddr, "Mohan");
page_cache_release(page);
}
up_read(¤t->mm->mmap_sem);
1，get_user_pages函数详解
https://liujunming.top/2017/07/03/get-user-pages%E5%87%BD%E6%95%B0%E8%AF%A6%E8%A7%A3/
2，页面的引用计数和get_user_pages
https://blog.csdn.net/iteye_5014/article/details/81824739
3，Linux Kernel get_user_pages() 源码分析
https://v1ckydxp.github.io/2020/04/22/2020-04-22-CVE-2016-5195%20%E6%BC%8F%E6%B4%9E%E5%88%86%E6%9E%90/
4，Direct IO 内核实现分析及揭示一个坑
https://blog.csdn.net/zancijun1666/article/details/83006205
5，澄清一个get_user_pages的事实
https://blog.csdn.net/dog250/article/details/5303268
6，get_user_pages的意义
https://blog.csdn.net/JK198310/article/details/89496618